Question

Propose a multi-step forward synthesis of target molecule (TM) from starting materials A and B (4 pts).

Answer 1

Answer on question#76521

We'll start with an **acid/base reaction** to deprotonate the terminal alkyne forming a good nucleophile.

\ce{ \chemfig{*6((-Acid)=-=(-H)=-)} + NaNH2 -> \chemfig{*6((-Na^+)=-=(-COOH)=-)} + H-NH-CHO} \text{ (conj. a} }

We need to elongate the chain by just one carbon. Let's give this methyl group a good leaving group to facilitate a quick SN2 reaction — my 'go-to' is Bromine, but you can also use Chlorine or Iodine.

$$\ce{ \chemfig{*6((-=(-O)=-=(-CH_3-Br)=-=(-S_N^2)=-=)} } \quad \ce{ \chemfig{*6((-CH_3)=-=(-CH_3)=-=)} }$$

Now that we have a carbon chain of desired length, let's carry out the acid catalyzed hydration.

$$\ce{ \chemfig{*6((-CH_3)=-=(-HgSO_4)=-=(-HgSO_4)=-=)} } \quad \ce{ \chemfig{*6((-OH)=-=(-enol)=-=)} }$$

But wait, the product is an enol, not a ketone!!

The next step will happen automatically. So while you don't have to show a reagent simply draw 'KET' over the reaction arrow for **Keto Enol Tautomerization**.

\ce{ \chemfig{*6((-OH)=-=(-enol)=-=)} \quad \ce{KET} \quad \ce{ \chemfig{*6((-Ketone)=-=(-ketone)=-=)} }

.